#include<iostream>
using namespace std;
//#define maxn 3
int main()
{
//	char ball[maxn]
	
//	int idx[3]={0,1,2};
	int w[3];
	for(int i=0;i<3;i++){
		cin>>w[i];
	}
	if(w[0]==w[1]){
		cout<<"C"<<endl;
	}else if(w[0]==w[2]){
		cout<<"B"<<endl;
	}else if(w[1]==w[2]){
		cout<<"A"<<endl;
	}else{
		cout<<"error"<<endl;
	}
	return 0;
 } 
